Hi all!

I am trying to run this minimal example of libtorch on Bela https://pytorch.org/cppdocs/installing.html , but I always run into the same error. I was wondering if someone had the same issue or might now how to approach it.

Regarding my setup: I am booting from a 64 GB SD card (I tried to run the same on EMMC but it ran out of disk memory). Compiling with g++ ran out of memory too (I guess RAM memory since I don't think it was taking the 64GB), so I tried using swap memory and got the same error as compiling with clang-7 (without swap memory)

Here is my folder structure:

example-app/
      example-app.cpp
      CMakeLists.txt

and example-app.cpp code:

#include <torch/torch.h>
#include <iostream>

int main() {
  torch::Tensor tensor = torch::rand({2, 3});
  std::cout << tensor << std::endl;
}

and CMakeLists.txt:

cmake_minimum_required(VERSION 3.0 FATAL_ERROR)
project(example-app)

set(DCMAKE_PREFIX_PATH "/root/Bela/projects/example-app/libtorch")
set(Torch_DIR "/root/Bela/projects/example-app/libtorch/share/cmake/Torch")
find_package(Torch REQUIRED)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${TORCH_CXX_FLAGS}")

add_executable(example-app example-app.cpp)
target_link_libraries(example-app pthread "${TORCH_LIBRARIES}")
set_property(TARGET example-app PROPERTY CXX_STANDARD 14)

To compile the project I do

mkdir build
cd build
cmake ..

which runs errorless
and then

cmake --build . --config Release

which gives me the following error with clang:

root@bela:~/Bela/projects/example-app/build# cmake --build . --config Release
Scanning dependencies of target example-app
[ 50%] Building CXX object CMakeFiles/example-app.dir/example-app.cpp.o
[100%] Linking CXX executable example-app
../libtorch/lib/libtorch.so: file not recognized: File format not recognized
clang: error: linker command failed with exit code 1 (use -v to see invocation)
CMakeFiles/example-app.dir/build.make:98: recipe for target 'example-app' failed
make[2]: *** [example-app] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/example-app.dir/all' failed
make[1]: *** [CMakeFiles/example-app.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2

and the following CMakeError.log:

Determining if the pthread_create exist failed with the following output:
Change Dir: /root/Bela/projects/example-app/build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_3bf71/fast"
/usr/bin/make -f CMakeFiles/cmTC_3bf71.dir/build.make CMakeFiles/cmTC_3bf71.dir/build
make[1]: Entering directory '/root/Bela/projects/example-app/build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_3bf71.dir/CheckSymbolExists.c.o
/usr/bin/cc     -o CMakeFiles/cmTC_3bf71.dir/CheckSymbolExists.c.o   -c /root/Bela/projects/example-app/build/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_3bf71
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_3bf71.dir/link.txt --verbose=1
/usr/bin/cc       CMakeFiles/cmTC_3bf71.dir/CheckSymbolExists.c.o  -o cmTC_3bf71 -rdynamic 
CMakeFiles/cmTC_3bf71.dir/CheckSymbolExists.c.o: In function `main':
CheckSymbolExists.c:(.text+0x4): undefined reference to `pthread_create'
CheckSymbolExists.c:(.text+0x8): undefined reference to `pthread_create'
CheckSymbolExists.c:(.text+0x20): undefined reference to `pthread_create'
CheckSymbolExists.c:(.text+0x24): undefined reference to `pthread_create'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
CMakeFiles/cmTC_3bf71.dir/build.make:97: recipe for target 'cmTC_3bf71' failed
make[1]: *** [cmTC_3bf71] Error 1
make[1]: Leaving directory '/root/Bela/projects/example-app/build/CMakeFiles/CMakeTmp'
Makefile:126: recipe for target 'cmTC_3bf71/fast' failed
make: *** [cmTC_3bf71/fast] Error 2

File /root/Bela/projects/example-app/build/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include <pthread.h>

int main(int argc, char** argv)
{
  (void)argv;
#ifndef pthread_create
  return ((int*)(&pthread_create))[argc];
#else
  (void)argc;
  return 0;
#endif
}

Determining if the function pthread_create exists in the pthreads failed with the following output:
Change Dir: /root/Bela/projects/example-app/build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_180e8/fast"
/usr/bin/make -f CMakeFiles/cmTC_180e8.dir/build.make CMakeFiles/cmTC_180e8.dir/build
make[1]: Entering directory '/root/Bela/projects/example-app/build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_180e8.dir/CheckFunctionExists.c.o
/usr/bin/cc    -DCHECK_FUNCTION_EXISTS=pthread_create   -o CMakeFiles/cmTC_180e8.dir/CheckFunctionExists.c.o   -c /usr/share/cmake-3.7/Modules/CheckFunctionExists.c
Linking C executable cmTC_180e8
/usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_180e8.dir/link.txt --verbose=1
/usr/bin/cc   -DCHECK_FUNCTION_EXISTS=pthread_create    CMakeFiles/cmTC_180e8.dir/CheckFunctionExists.c.o  -o cmTC_180e8 -rdynamic -lpthreads 
/usr/bin/ld: cannot find -lpthreads
clang: error: linker command failed with exit code 1 (use -v to see invocation)
CMakeFiles/cmTC_180e8.dir/build.make:97: recipe for target 'cmTC_180e8' failed
make[1]: *** [cmTC_180e8] Error 1
make[1]: Leaving directory '/root/Bela/projects/example-app/build/CMakeFiles/CMakeTmp'
Makefile:126: recipe for target 'cmTC_180e8/fast' failed
make: *** [cmTC_180e8/fast] Error 2

I don't think the problem is cannot find -lpthreads since I tried adding find_package(Threads) to the CMakeLists and it did find the package (-- Found Threads: TRUE)

A similar error is reported in https://stackoverflow.com/questions/31948521/building-error-using-cmake-cannot-find-lpthreads/57371779#57371779 and it is apparently due a version missmatch, but in my laptop it ran errorfree and did not complain about versions...

any ideas?